1. Field of the Invention
The present invention relates to a power conversion system, in particular, to the power conversion system introducing a zero-voltage switching mechanism to suppress the system from a surge current, and further to a zero-voltage start-up device.
2. Description of Related Art
For suppressing the surge current as starting up a power conversion system, and enhancing stability of power supply circuit as starting, the conventional power conversion system is provided. Such as the system shown in FIG. 1, the system includes an electromagnetic interference suppression unit 101, a standby circuit 105, a power conversion circuit 107, and a bridge rectifier 119. The electromagnetic interference suppression unit 101 is used to suppress the whole circuit from the EM interference caused by the input power supply Vin. A power factor correction unit 103 and a small capacitor 109 may be included to correct the power factor and adapted to the circuit with large load.
When the power conversion system plugs to the input power supply Vin and a switching unit 115 is not yet turned on. That means the electronic device at the back end load does not function. Meanwhile, the input power charges the storage capacitor 111 via a diode D, and the device stays in standby and provides standby power to the back end load. Therefore, the load may operate as standby state.
When a user starts up the back end load, the switching unit 115 is turned on firstly. Meanwhile, an input power Vin is supplied to the power factor correction unit 103, the storage capacitor 111, and the power conversion circuit 107 via the switching unit 115 and a surge suppression unit 117, a bridge rectifier 119 and a small capacitor 109. This conventional scheme adopts the surge suppression unit 117 to prevent the whole power conversion system from the damage caused by a large current from the input power Vin.
Next, when the current is getting stable, the switching unit 115 connected to the surge suppression unit 117 is turned on, and the input power Vin is routed through the path of the switching unit 115 in order to supply power to the circuits in the power conversion system. The surge suppression unit 117 will not continuously consume the power as it shorts the circuit after the input power current is stable. Therefore, the scheme may save the power consumption.
However, the conventional scheme needs the switching unit 115 to turn on or turn off the circuit for suppressing the surge current. Thus an additional device is required to drive the switching unit 115, and the driver (not shown) will increase the cost.